Urodynamic effects induced by intravesical capsaicin in rats and hamsters

This study compared the effect of acute intravesical capsaicin administrati on on transvesical cystometries in urethane-anesthetized rats and hamsters, and aimed to assess whether sensory neuropeptides (tachykinins; calcitonin gene-related peptide, CGRP) play a role in the urodynamic effects of capsa icin in these species. The following urodynamic parameters were evaluated: the mean micturition interval (MI), the pressure threshold for micturition (PT), and the mean amplitude of micturition contractions (MAC). Two concent rations of capsaicin (10 and 100 muM) were evaluated in both species. Here, we demonstrate that 10-muM capsaicin decreased the PT in both rats and ham sters, and 100-muM capsaicin decreased the PT in hamsters and decreased the MI in both species. In addition, 100-muM capsaicin increased the MAC in ra ts but decreased the MAC in hamsters. Administration of CGRP (10 nmol kg(-1 ), i.v.) significantly decreased both MAC and PT in hamsters only, while ca psaicin-induced desensitization of neuropeptide-containing afferents antago nized the urodynamic effects of intravesical capsaicin. In addition, admini stration of the tachykinin N-K-2 receptor antagonist, Nepadutant (100 nmol kg(-1), i.v.), reduced the effects of capsaicin (100 muM) only in rats. The se results indicate that capsaicin induces bladder hyperactivity in both ra ts and hamsters, but the urodynamic characteristics of this hyperactivity m arkedly differ in these two species. The differences observed may be due to differential expression of sensory neuropeptides in capsaicin-sensitive bl adder afferents or neuropeptide receptors in smooth muscle cells and in ner ve fibers. (C) 2001 Elsevier Science B.V. All rights reserved.